1. Field of the Invention
The present invention relates to an inkjet printer.
2. Description of Related Art
As a kind of recording apparatus for recording information on a recording medium such as a sheet of paper, there is known an inkjet printer that ejects ink droplets onto a recording medium to record information. Such an inkjet printer includes an actuator, a printhead, and a maintenance unit including a purge cap. The printhead has ink passages formed therein, and a nozzle surface where a plurality of nozzles for ejecting ink droplets therefrom are arranged. In the inkjet printer, the printhead is movable between a recording area and a purge area adjacent to the recording area. The printhead performs printing on the recording medium while reciprocated across the recording area. The printhead is located at the purge area when a purging operation is performed with the nozzle surface covered with the purge cap so that the purge cap receives ink discharged or sucked from the nozzles for purging.
In the printhead for the inkjet printer, the nozzle surface is usually constituted by an external surface of a nozzle film that is coated with a water repellent material. The nozzle film is formed of polyimide, for instance. In such an arrangement, the nozzle surface is brought into frictional contact with the recording medium, and the water repellent coating and the nozzle film tend to be damaged. Recently, to meet a demand for a higher print rate, the size of the nozzle surface has been increased, thereby further increasing the risk of damage of the nozzle film and the water repellent coating thereon.
As a technique for coping with this disadvantage, there is known an arrangement where the nozzle surface is covered with a metallic cover plate, except at and around a row of the nozzles, so as to constitute a front surface of the printhead by the cover plate and a part of the nozzle surface as exposed through a through-hole formed in the cover plate, as disclosed in JP-A-5-201000 (especially paragraphs 0020, 0021 and FIGS. 1 and 2), for instance.
Since the cover plate has such a through-hole, ink remaining on the front surface can not be completely removed when the front surface is wiped with a wiper immediately after a purging operation.
After a purging operation, a mixture of small bubbles and ink droplets is inside the purge cap. At a moment when the purge cap is separated from the front surface of the printhead, this mixture is drawn into a nozzle because of a negative pressure in the printhead. The bubbles contained in the mixture and drawn into the nozzle thereafter remain in the ink passage extending from that nozzle, thereby attenuating a pressure wave which is generated in the ink passage when the actuator is driven to eject an ink droplet from the nozzle, during a printing operation. Hence, stability can not be assured in ejection performance of the printhead.
As a countermeasure to the instable ejection performance, deaerated ink is used in the inkjet printer so that the bubbles introduced into the nozzles are dissolved in the deaerated ink to restore the ejection performance. However, it takes some time to dissolve the bubbles in the ink, and thus it is necessitated to wait until the time elapse before the next printing is started.